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Subacromial impingement

Subacromial impingement is very common.
The
supraspinatus muscle and tendon
run under the acromion and attach onto the
greater tuberosity of the
proximal humerus.
If you look at an X ray of the shoulder you will see "the ball" is not a perfect
circle, the greater tuberosity works a little like an off set cam, in that if
you rotate the arm upwards, the space under the acromion (subacromial space) reduces.
This space is not empty this is where the
supraspinatustendon runs.
The
tendon then gets pinched (impingement) leading to pain.

I often describe sub acromial impingement in this slightly oversimplified
manner, it is more than just a mechanical problem.
As the tendon ages the blood
supply deteriorates, the ageing tendon degenerates and thickens (tendinopathy).
It is not a purely inflammatory condition although we talk about supraspinatus
tendonitis it is often more a degenerative process of tendinosis.

Diagnosis
The diagnosis is made on a history of deep seated shoulder pain that may affect
sleep.
The pain is often felt radiating down the side of the shoulder over the deltoid
muscle and occasionally
running down the front into biceps.
Pain right over the top of the shoulder is
often coming from the acromiclavicular joint (ACJ).
Pain above and behind the shoulder in the region of trapezius is often related
to the neck or muscular in relation to overuse of the parascapular muscles.

The pain is made worse with overhead activities and extending the shoulder
behind your back, for example putting on a jacket or reaching into the foot well
at the back of the car.
On examination full movement of the shoulder is possible but painful in the zone
of impingement.
The zone of impingement or painful arc is where below shoulder height the
shoulder is reasonably comfortable, when elevating the arm as it gets closer to
shoulder height the pain increases being felt radiating into the deltoid.
Once the arm is
above shoulder height the pain reduces slightly.
However when you lower the arm again, the pain returns at the level of shoulder height

Painful arc - The painful arc is this pain felt from around 60°
elevation to 130°, particularly the pain improving slightly when you get above
shoulder height.

Impingement testing, if you elevate your arm to 90° and then twist it, it
increases the pain.
Sometimes there may be a little weakness of the shoulder
related to pain or a tear in the rotator cuff (see
rotator cuff tear).

X rays are requested to see if there is any signs of arthritis in the joint, to exclude any calcification in the tendon (see
calcific
tendonitis) and to look for bony abnormalities around the shoulder (see
os
acromionale).

An MRI scan or
ultrasound sound scan may
be requested to have a look at the soft tissues, particularly the rotator cuff
to see if there is a tear in one of the tendons in the rotator cuff.
An MRI and or ultrasound is not always needed.

TreatmentTreatment is predominantly non operatively in the first instance. Around
80% of patients with acute onset of shoulder pain due to impingement or
tendonitis will get better with non operative treatment within 6 months and not
need any further intervention.
Surgery is only indicated if the symptoms don't resolve with 6 months of non
operative treatment.
Non operative treatmentThe main stay of non operative treatment involves
Time/ Rest - relative rest
Pain killers - particularly Non steroidal anti-inflammatories
Physiotherapy
Injections

Time/ Rest - Relative rest
Doing nothing is just as bad as doing too much, it is important to keep
the shoulder moving so that it does not stiffen up and go onto a frozen shoulder.
Similarly continually hammering the shoulder and the tendons around the shoulder
will perpetuate the impingement and swelling of the tendon.
Keep stretching the shoulder over shoulder height but avoid doing too much and
avoid stressing the shoulder repeatedly particularly in the zone of
impingement.

Pain killers
The best pain killers if you can tolerate them are the non steroidal
anti-inflammatories (NSAIDS).
The pain killers are not only important in
reducing the inflammation, but also preventing the pain spasm cycle. In response
to pain all the muscles around the shoulder tighten up. The tense muscles then
altering normal motion at the ball and socket joint and the shoulder blade.
Hence if the NSAID's are not controlling your pain it is important to add other
pain killers to control the pain. (See
pain killers).

Physiotherapy
Physiotherapy is important to keep range of motion in the shoulder and keep the
muscles around the shoulder balanced and working together.
It is not about 5 or 10 minutes with a physiotherapist but getting into a
regular rhythm of stretches and exercises every day.

Stretches to avoid posterior capsular tightness is important, so the ball can
roll smoothly. Rehabilitating the 4 rotator cuff muscles is important so they
can ensure smooth movement of the ball and keeping the humeral head (ball) well
centred on the socket. It is not about just doing random exercises it is
very important to balance the forces around the shoulder.

Injections
There are several different kinds of injections around the shoulder.
Unfortunately none have been shown to be a miracle cure.
Steroid (cortisone)
injections are very good for reducing inflammation and swelling but not very
good for tendon healing.
In the past they were probably over used.
Now a days I
would offer 1 maybe 2 injections but no more as repeated injections around the
cuff can soften the tendon and lead to tendon rupture.
The injection should be around the tendon and not into the tendon.

Investigators are still looking for more effective injection treatments eg.
platelet rich plasma.
There are several ways of injecting the shoulder from the front, the side
and from the back.
I inject from the back minimising the risk of injecting into
the tendon.
If the main problem is the biceps tendon then the injection is from the
front under ultrasound guidance
Often the thought of the injection is worse than the reality.
A steroid
injection often leads to a deep seated ache for 24 hours and then may take 4 to
6 weeks to reach full effect.

Operative treatment
Surgery is only indicated if non operative measures have failed.
Surgery involves a subacromial decompression - removing the spur on the
under surface of the acromion and making more room in the subacromial space for
the tendons.
A sub acromial decompression may be done open or arthroscopically.
At 6 months
there is no difference in the final outcome, however in the short term
arthroscopic or keyhole surgery is better tolerated.
An arthroscopic sub acromial decompression can be done as a day case or
overnight stay.
On average the shoulder is improved by 60 to 80%, it is possible to shave away a
little bone, but not take it all away as acromion is the anchor point for the
deltoid - The power horse of the shoulder.

All surgery is associated with risk.
The risks generally being those of a general anaesthetic, infection risks <1:1000, stiffness,
incomplete resolution, recurrence, frozen shoulder,
nerve injury.

With keyhole surgery it is possible to see all of the shoulder and look for any
rotator cuff tears or damage to the tendons and ligaments around the shoulder.
If damage is found to the rotator cuff it can often be dealt with at the same
sitting arthroscopically (see
rotator cuff tear)
In general range of motion returns at around 6 weeks, but it may take up to 3
months to feel the real benefits of pain relief. The shoulder will often
continue to improve even a year to 18 months after the surgery.